Does it kinda sound like a ticking at all? If you have replaced your spark plugs or coil packs recently double check they were tightened to proper torque spec. When they arent spec'd properly they can cause an slight engine tick sound.

Other causes include oil taking to long to reach the lifters which causes the lifters to tick. Being your in California I dont see this one as much of a possibilty.

The one I think it most is, is your VANOS system. What the Vanos does is advanced the timing of the intake cam for optiminal performance. However the unit has seals and a bearing that can go bad. With only 50k miles on it, it shouldnt be going already, but it is possible.